This is a continuing study of the genetics of the histocompatibility systems, erythrocyte antigen systems and the control of the immune respone with particular emphasis on the development of the rabbit as a more effective model for research in the transplantation of organs, tissues or cells. Other polymorphic systems are being investigated to serve as chromosomal markers for genes involved in immunogenetic processes but which are not easily identified. The systems are being used to study the mechanisms which affect the persistence and proliferation of cells following the induction of tolerance chimera formation, skin graft or tumor graft rejection.